In a statement explaining why the app was removed, Apple pointed to its inclusion of nude images and said that it has received complaints from users about possible child pornography.

"The app was removed from the App Store for featuring pornographic images and material, a clear violation of our guidelines," said an Apple spokesperson. "We also received customer complaints about possible child pornography.

"We've asked the developer to put safeguards in place to prevent pornographic images and material in their app."

500px has responded by defending its policies, pointing out that the only nude images on the service are "artistic" in nature and can be filtered out using the programme's search function.